Drilling fluid

ABSTRACT

A chemically oxidized starch drilling fluid dispersant having improved resistance to deterioration in the presence of bacteria in a low pH mud system by heating a chemically oxidized starch dispersant for 15 to 50 minutes at temperatures of 400*-475* F. and an aqueous drilling fluid containing the heated chemically oxidized starch dispersant.

United States Patent Kolaian [451 Jan. 25, 1972 [54] DRILLING FLUID2,557,473 6/1951 Ryan ..252/8.5 2,951,776 9/1960 Scallet et al....252/8.5 [72] Inventor: Jack H. Kolalan, Wappmgers Falls, NY.3,232,871 2/1956 Walker et "252/85 7 Assignee: Texaco Inc" New York N Y'3,492,227 1/1970 Kolaran ..252/8.5 3,493,561 2/1970 Kolaian et a1..260/233.3 [22] Filed: June 30, 1969 Primary Examiner-Herbert B. Guynnl A l. N 8 7 [2 1 pp 0 3 AnorneyK. E. Kavanagh and Thomas H. Whalley[52] U.S. Cl. ..252/8.5 C, 127/33, 127/71, [57] ABSTRACT 2 [51} Int Cl 30 A chemically oxidized starch drilling fluid dispersant havmg [58]Field iiiiiiiiiiiiiiiiiiiii 252 5 27/33 improved resistance todeterioration in the presence of bac- 260/233 teria in a low pH mudsystem by heating a chemically oxidized starch dispersant for 15 to 50minutes at temperatures of [56] Reterences Cited 400-4751r f. and anaqueous drilling fluid containing the heated chemically oxidized starchdispersant.

4 Claims, No Drawings DRILLING FLUID The present invention relates to animproved drilling fluid dispersant, an aqueous drilling fluid containingthe improved dispersant and an improved drilling fluid additivecomposition.

In commonly assigned U.S. Pat. No. 3,417,017, issued Dec. 17, 1968,there is disclosed and claimed an aqueous drilling fluid containing claysolids dispersed therein and a chemically oxidized starch dispersantproduced by oxidizing starch with a water soluble inorganic oxidizingagent in an aqueous acidic reaction medium with at about 75-l50 F. forabout 2-75 minutes and drying the resultant oxidized starch dispersant.1n commonly assigned, copending application Ser. No. 741,214, filed June28, 1968 now U.S. Pat. No. 3,493,561, there is disclosed and claimed themethod of making the oxidized starch dispersant by oxidizing starch witha water soluble inorganic oxidizing agent in an aqueous acidic reactionmedium at about 75l50bL F. for about 2-75 minutes and drying theresultan oxidized starch product.

A disadvantage of this chemically oxidized starch product as adispersant in a low pH mud system is its susceptibility to attack bybacteria with the result that an objectionable, sour odor is emittedfrom the mud. Further the dispersing properties of the starch productare not outstanding in such low pH mud systems. It is known that theaddition of a starch preservative such as formaldehyde in amounts of theorder of about one-sixth pound per barrel of drilling fluid to adrilling fluid will prevent or inhibit the development of ofi'ensiveodors therein due to deterioration of the starch component by bacteriaattack.

It has now been found that this oxidized starch dispersant can beimproved with respect to its susceptibility to deteriora tion in thepresence of bacteria with a resultant inhibition of the objectionablesour odor in a low pH mud system by subjecting the dried oxidized starchdispersant to further heating for a period of from about 15 to 45minutes at temperatures between about 400 and 475 F. with agitation.

Exposure of the dried chemically oxidized starch dispersant to theserelatively high temperatures for the indicated time periods does notadversely effect the dispersing properties of the material in low pH mudsystems. Surprisingly, such heat treatment improves the dispersingproperties of the resulting heat treated starch product in shale controlmud systems. This is in contrast to the adverse effects on itsdispersing properties in both mud systems if the oxidized starch issubjected to such high temperatures in the initial drying step forperiods over about 5 minutes.

In the method of the present invention the use of heating temperaturesabove about 475 F. has an adverse effect on the dispersing properties ofthe material while temperatures below about 400 F. do not produce thedesired result in terms of making the starch product resistant tobacterial attack while maintaining satisfactory dispersing properties.Similarly, time periods above about 50 minutes and below about minutesdo not produce the desired results.

The chemically oxidized starch dispersant used as the starting materialin the present invention is more fully described and claimed inapplicants copending application Ser. No. 741,214, filed June 28, 1968,and is hereby incorporated herein by reference. Applicants U.S. Pat. No.3,417,017, issued Dec. 17, 1968, discloses and claims use of theoxidized starch dispersant in aqueous drilling fluids and as a drillingfluid additive. The disclosure of said patent is also expresslyincorporated herein by reference.

Following is a description by way of example of a method of carrying outthe present invention.

COMPARATIVE EXAMPLE A Argo brand, food grade, corn starch in an amountof grams was slurried with 38 milliliters of an aqueous 0.5 M nitricacid solution and heated to a temperature of 120 F. There was added tothe heated slurry l3 milliliters of an aqueous 0.2 M sodium dichromatesolution and mixing was continued. The temperature of the resultingmixture was increased to about 140-150 F. and maintained at thistemperature for about 30 minutes. The crude reaction product was removedfrom the reaction vessel by pouring the contents onto a steel plateheated in a forced air drying oven to form thereon a relatively thinlayer of about one-eighth inch or less in height of the oxidized starchproduct. The heated steel plate now containing the crude reactionproduct was then heated additionally for about 5 minutes at an oventemperature of 300-325 F. The plate containing the dried reactionproduct was removed from the oven, allowed to cool to room temperatureand the reaction product removed therefrom. The reaction product waspulverized and there was obtained a light green colored powder. Theproduct yield was about percent on a dry starch basis.

The starch product of this example was found to be susceptible to attackby bacteria when employed as a dispersant in a low pH mud system. Themud system was a top hole base mud obtained from West Cote Blanche Bayarea having the following properties was used as the initial mud in allcases: V 53, V 39, PV 14,YP 25, AV 26, Gels at 0 and 10 minutes, 7 and18, respectively, pH 9.0, API Water Loss (30 min.) 13.0.

EXAMPLES 1-4 In each of these examples, a portion of the chemicallyoxidized starch dispersant of comparative example A was heated for aprescribed time period with agitation by stirring at a prescribedtemperature. Thereafter the resulting treated starch dispersants wereincorporated in a low pH drilling fluid in an amount of 3.5 pounds perbarrel plus 1 .9 pounds per barrel of sodium hydroxide. The mud was agedovernight in an oven at F., before testing. The odor tests were afterabout 3 days time. The properties of the drilling fluid were determined.The heating times, temperature and odor test results are tabulated belowin table 1.

Inspection of the results in table 1 above shows that heating thechemically oxidized starch dispersant of comparative example A for 15-60minutes at 400450 F., examples 1, 2, and 4 results in a product thatdoes not sour in a low pH mud system. The product of comparative exampleA, no heating after drying, resulted in a sour odor from the low pH mud.The product of example 3, heated for 15 minutes at 500 F., outside therange of the invention, also produces a nonsouring product in a low pHmud but is satisfactory since the dispersing properties of the materialare destroyed by such treatment. Table 2 below shows this adverseeffect. Similarly, the product of example 4, heated for 60 minutes at400 F., is classified as not acceptable because its dispersingproperties in a shale control mud system are not satisfactory. Table 2shows these poor mud test data.

In table 2 below the shale control mud was prepared by adding to thebase mud, 3.5 pounds of the particular dispersant 0.3 pound of sodiumhydroxide, 0.3 pound of lime and 3.0 pounds of calcium chloride perbarrel. The mud was aged overnight in an oven at 140 F.

TABLE 2 Low pH mud Shale control mini Shearometer Shearorneter gels,lbs. gels, lbs./ Dis- Tem- Approx- 100 ft. Approx- 100 It. persantperaimate imate amount, Time, ture, viscos- 10 viscosl0 lbs./bbl. minsP.V. Y1 ity, cpe. min min. 1.V Y.P ity, cpe'. min. min.

Control Example 7 A 12 0 12 O 0 A 3. 26 0 26 0 0 Example 1 7 400 0 13 00 l 3. 5 15 400 26 0 )3 0 0 I Example 2,. l 7 15 450 0 14 0 0 l 3. 5 15450 18 2 1) 0 0 Example 3 .5 7 15 500 21 15 28. 5 0 3. 5 l 3. 5 15 50010 70 45 0 18 Example 4 7 60 400 14 1 14. 5 0 l 3. 5 00 22 6 25 0 0Inspection of the data in this table 2 shows that the dispersingproperties of the products of examples 1 and 2 are improved by the heattreatment method of the present invention as evidenced by the respectivegel strength data. A comparison of the yield point and gel strengthvalues of these examples with the values obtained using the product ofcomparative example A show that the lO-minute gel strengths areconsiderably lower, indicating more effective dispersing effects. Thehigh-yield point and gel strength data for the product of example 3 showthat a heating temperature of 500 F. results in a deterioration of theproducts dispersing properties in both mud systems.

The data shown for example 4 show that for a heating time of 60 minutesat 400 F., some deterioration in dispersing properties results in theshale control mud as evidenced by the increase in yield point andIO-minute gel strength values.

Obviously, many modifications and variations of the invention ashereinbefore set forth may be made without departing from the spirit andscope thereof, and therefore, only such limitations should be imposed asare indicated in the appended claims.

I claim:

1. An aqueous drilling fluid containing clay solids dispersed thereinand a chemically oxidized starch dispersant produced by oxidizing starchwith a water soluble inorganic oxidizing agent selected from the groupconsisting of permanganates, chromates, dichromates, chlorates,chlorites, hypochlorites, bromates, hypobromites, peroxides,peroxodisulfates, hypochlorous acid and peroxodisulfuric acid which ispresent in an amount of from about 0.04 to about 0.5 gram atom ofavailable oxygen per grams of starch reactant in an aqueous acidicreaction medium selected from the group consisting of nitric acid,hydrochloric acid, sulfuric acid, acetic acid, propionic acid,benzenesulfonic acid and toluenesulfonic acid wherein the acid reactantis present in an amount of from about 4.5 to about 220 percent by weightper part by weight of starch at a temperature in the range of from about75 F. to about F. and below the gel temperature of the starch in thereaction medium for a period of time between about 2 minutes and about75 minutes and sufficient to oxidize said starch material, drying theresulting oxidized starch, and thereafter heating said dried oxidizedstarch at a temperature of from 400 to 475 F. for 15 to 50 minutes, saidresulting heated starch dispersant being present in the drilling fluidin 2. A drilling fluid as claimed in claim I wherein said resultingheated oxidized starch dispersant is present in an amount between 0.5and 7.5 pounds per barrel of fluid.

3. An aqueous drilling fluid as claimed in claim 1 wherein said oxidizedstarch reaction product is neutralized with an alkaline reagent to a pHin the range of from about 4 to 7 before drying.

4. An aqueous drilling fluid as claimed in claim 1 wherein the heateddried oxidized starch dispersant has a water content of from about 3 to6 percent by weight.

UNITED STATES PATENT OFFICE CERTEFRATE 6F CGRRECTIQN Patent No. 3 37A93Dated January 25, 1972 Inventor(s) Jack H. Kolaian It is certified thaterror appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

irst page, Abstract Should be lO0-475 F.-- 301. 1, line 11 Omit "with" o1 Col. 1, line 18 Should be -.--75-150 F Col. 2, Table 1 Under Example1, move 15 to next column. e 001.. 2, line 6 Change "satisfactory" to--unsa.tis-

factory-- Signed and sealed this 1st day of August 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JRQ ROBERT GOTTSCHALK Attesting Officer Commissionerof Patents *zgz gy UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTIUNPatent No. 3 37 93 Dated January 25,197;

Inventor(s) Jack H- Kolaian It iscertified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

- irst a. e, Abstract Should be l00- +75 F.--

201. 1 fiine 11 Omit "with" Col. 1, line 18 Should be -.--75-150 F Col.2, Table 1 Under Example 1, move 15 to next column. C01, 2, line 6 4Change "satisfactory" to --unsa.tis

factory-- Signed and sealed this 1st day of August 1972. I

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissionerof Patents

2. A drilling fluid as claimed in claim 1 wherein said resulting heatedoxidized starch dispersant is present in amount between 0.5 and 7.5pounds per barrel of fluid.
 3. An aqueous drilling fluid as claimed inclaim 1 wherein said oxidized starch reaction product is neutralizedwith an alkaline reagent to a pH in the range of from about 4 to 7before drying.
 4. An aqueous drilling fluid as claimed in claim 1wherein the heated dried oxidized starch dispersant has a water contentof from about 3 to 6 percent by weight.